The HARC Center has engaged in a significant number of collaborations, both with members of the existing CHEETAH and PCHPI Centers and with members of the broader HIV and structure communities. Our systems-to-structure approach has lent itself naturally to extensive interactions, with particular excitement over the global HIV proteomic results. For example, Wes Sundquist and collaborators in CHEETAH have analyzed the set of Gag interacting proteins, which is not a focus of the HARC Center biology, and have uncovered several exciting viral phenotypes, established biochemical interactions, and solved the crystal structure of one interacting domain. Our goal is to emulate this paradigm to the greatest extent possible, by engaging even more of the HIV community, as well as those studying areas of host cell biology that pertain to possible connections to HIV. We propose three mechanisms to accomplish this: First we will continue outreach efforts with known investigators working in areas related to the Center projects on the viral accessory and regulatory proteins, or on technology development. The current panel of collaborations is described below. Second, we will establish a Collaborative Opportunity Fund, with an emphasis on encouraging new or non-HIV investigators to apply for funding with ideas relevant to the Center, as detailed below. Third, if Center funding is renewed, we propose to mobilize the other HIV Structure Centers to host a joint international symposium at UCSF focused broadly on HIV-host interactions. In that context, we hope to define any new emerging areas relevant to the structural biology of the interactions, with a wide net cast that might lead to extended collaborative efforts, perhaps in the broader contexts of host-pathogen interactions or drug design and possibly with other NIH-funded Center initiatives.